Heat exchangers



June 17,11969 I w. FIENI 3,450,197

HEAT EXCHANGERS `une 17, 1969 w. FIENI 3,450,197

HEAT EXCHANGERS Filed Feb. s. 196e sheet 2 of s June 17,*1969l w. F|EN| 3,450,197

HEAT EXCHANGERS Filed Feb. 196e sheet 5 of s J4 llllllllllllllllllllllll'lllllTl---/l 320 58 Fig. 6

United States Patent O 3,450,197 HEAT EXCHANGERS Walter Fieni, Paris, France, assignor to Societe Anonyme Francaise du Ferodo, Paris, France, a company of France Filed Feb. 3, 1966, Ser. No. 524,775 Claims priority, application France, Feb. 6, 1965, 4,664; Jan. 25, 1966, 47,205 Int. Cl. F01p 7/14; F28f 27/02, 13/06 U.S. Cl. 16S- 142 3 Claims ABSTRACT OF THE DISCLOSURE This invention relates to a device of the kind in which a first fluid circulating at a velocity which may vary or be varied within a 4wide range is placed in heat exchange relationship with a second iluid. It concerns in particular a device in which the exchange of heat is effected through the walls of one or more conduits through which the rst fluid passes, the said walls being swept by the secondary fluid, which flows transversely to the direction of ow of the first fluid in said conduit or conduits.

Devices of this kind are used in particular for heating motor vehicles and in this instance comprise an exchanger of the finned tubular type through which a ow of hot water passes longitudinally and which is traversed transversely `by the air for Ventilating the vehicle interior. In very cold weather, the hot water is delivered to the exchanger at a high rate of ow and the exchanger is designed so that the air is eiciently heated from` one side of the exchanger to the other. The stream of air entering the interior space of the vehicle is thus heated in a substantially uniform manner throughout its cross-section.

When it is desired to heat the vehicle in slightly cool weather, the exchanger is supplied with hot water at a considerably lower rate of flow, for example not more than 1/25 of the rate of flow used when the weather is very cold. As a result, the air is heated only in the vicinity of the exchanger inlet since at the much lower rate of flow the hot water loses its heat before flowing very far through the exchanger, so that the side of the exchanger which is remote from the inlet does not effect any heating of the passing air. This drawback is at least partlyV alleviated when the heating system includes a fan drawing the air through the exchanger, because the fan mixes the air drawn in, but the drawback is particularly noticeable when there is no fan or 4when a fan blows the air through the exchanger.

It is appropriate also to explain that if the exchanger were to be designed so that the velocity of circulation of hot water at a low rate of flow was sufiicient to heat the exchanger from one side to the other, such exchanger would operate with an excessive loss of pressure when supplied -with hot water at a high rate of flow.

It will be readily understood that diculties of the same nature occur in many exchangers of the kind described in which the rate of flow of primary fluid is liable to vary or can be varied within a wide range.

In the exchanger according t-o the present invention, which is supplied with the rst fluid through a main inlet, on one side, one or more auxiliary supply conduits for the first iluid are provided which terminate in the exchanger in a zone remote from the main inlet, so as to create in this zone of the exchanger, at low rates of flo-w, a circulation of the first fluid substantially at the inlet temperature, without appreciably disturbing, at high rates of flow, the ow through the exchanger of the fluid entering by the main inlet.

Thus, in the case of a vehicle heating device, the invention enables the exchanger to be heated on both sides, for example in the Vicinity of both ends of its circulation conduits, when the iirst fluid is circulating at a low rate of flow, without appreciably reducing the efficiency of the exchanger when it is operating at a high rate of flow.

The auxiliary supply conduit is advantageously -given a resistance distinctly higher than that of the main inlet, for example by throttling or constructing such auxiliary supply conduit. In one embodiment, the exchanger comprises a nest of circulation tubes terminating at one end at an exchanger side piece divided into two headers, one of Iwhich is connected to the main inlet and the other to the outlet for the rst fluid, and at the other end at a second side piece, on the side of the exchanger `remote from the first side piece, forming a single intermediate header, the auxiliary supply conduit opening into the said intermediate header preferably in a position which is olf-set with respect to the main inlet.

The auxiliary supply conduits may be constituted by tubes disposed inside the exchanger and for immersion in the iirst fluid in such manner as to convey a part of the first fluid coming from the main inlet towards the side of the exchanger remote therefrom. The first iluid is thus divided into a lirst stream which passes outside these auxiliary supply tubes and a second stream which passes through them and mixes with the rst stream downstream of the said auxiliary tubes. The latter tubes are preferably of thermally insulating material being made, for example, of plastics material, so that the second stream enters the mixing zone at the highest possible temperature.

The description which follows with reference to the accompanying drawings, which are given by way of nonlimitative example, will make it clearly understood how the invention can be carried into effect, the details appearing both from the drawing and from the text indicating further inventive features.

In the drawings:

FIGURE l is a view in longitudinal section of one embodiment of heat exchanger in accordance with the invention;

FIGURE 2 is a cross-sectional view of the exchanger of FIGURE l;

FIGURES 3 and 4 are diagrammatic views respectively showing, in longitudinal section, another two embodiments of heat exchanger;

FIGURE 5 is a cross-sectional view on a larger scale on the line V-V of FIGURE 4;

FIGURE 6 shows diagrammatically in longitudinal section a modified form of the exchanger of FIGURE 1.

The exchanger of FIGURES l and 2 has the conventional structure of a heating device for motor vehicles and comprises a nest` of tubes (generally indicated at 1 in FIG. 2) of flattened cross-section and having fins 2. These tubes 1 are xed to the tube walls 3, 4 of two side pieces 5, 6.

In the embodiment illustrated, the side piece 5 is divided into an inlet header 7 and an outlet header 8 provided with a water outlet 9. The hot water forming the rst fluid arrives under pressure through a pipe 10 which feeds the normal inlet tube 11 terminating in an inlet orice 11a in the header 7. The exchanger is designed so that, in very cold weather, the hot water arriving at a high rate of iiow through the pipe 10 and passing through the tube 11,

the header 7 and the corresponding tubes 1a of the nest into the intermediate header formed by the side piece 6, and from here through the other tubes 1b into the outlet header 8, efficiently and evenly heats the air for Ventilating the vehicle, which air passes transversely between the tins 2.

In accordance with the invention, the hot water pipe 10 also feeds an auxiliary supply pipe 12. This auxiliary pipe is constricted by a restriction 13 and terminates at the intermediate header 6.

In use during moderate weather, when the pipe 10 is supplied with hot water at a very low rate of ow, which may drop to 1/25 of the rate of flow used in very cold weather, the exchanger being located in a normal stream of air, the air sweeping over the tubes 1a is heated in the vicinity of the header 7 but very little in the vicinity of the header 6, whilst the air sweeping over the tubes 1b is heated in the vicinity of the header 6. Thus, relatively even heating of the Ventilating air is achieved even at a low rate of supply of hot water. At a high rate of ow, that is to say under conditions of great cold, the exchanger operates as hereinbefore indicated, and the entry of hot water through the auxiliary pipe 12 does not appreciably disturb the circulation of the hot water entering through the tube 11 and issuing through the outlet 9.

It will be observed that the restriction 13 imposes on the flow through the auxiliary pipe a loss of pressure which is proportionally higher at a high rate of flow than at a low rate of flow. It is probable that this feature contributes, atleast in part, to the advantageous effects which have been found. It has also been found that, by modifying the cross-section of the restriction 13, it is possible to obtain at will either the same air temperature on both sides of the exchanger or a higher temperature on the right than on the left or Vice versa.

The following advantageous effect has been obtained in the tests carried out on an exchanger in accordance with FIGURES 1 and 2, the scale being given by the measurement a of the distance between the tube walls 3, 4, which was equal to 220 mm. The opening of the restriction 13 had a diameter of 5 mm., the tube 11 had an internal diameter of 8 mm. and the outlet 9 had an internal diameter of 16 mm.

When the pipe 10 was supplied with hot water at a rate of flow of 500 litres/hour, the exchanger was heated normally and heated the Ventilating air of a conventional motor car with good efficiency. When the pipe 10 was supplied with hot water at a rate of flow of 20 litres/ hour, the exchanger was heated in the vicinity of each of the tube plates 3 and 4 and heated in a substantially even manner the Ventilating air leaving on the right of the exchanger and that leaving on the left.

The exchanger shown diagrammatically in FIGURE 3 is of the elongated type and comprises a single tube having ns 15a and swept transversely by the air to be heated. The auxiliary conduit is constituted by a tube 18 shorter than the tube 15 and which is disposed inside the latter in such a manner as to open at 19 into an intermediate zone between the ends of such tube 15. The upstream end of the tube 15 is connected in fluid-tight fashion to the tube 18, the latter being connected to the inlet 16 for the rst fluid and its upstream portion being provided with orifices 20. A constriction 21 is provided in the tube 18.

At a low rate of iiow, the first iiuid entering at 16 is divided into a rst stream, which passes through the orices into the annular passage between the tubes 15 and 18 and is cooled therein, heating the air passing across the left-hand part of the exchanger, and a second stream which flows through the tube 18 and arrives in a hot state at 19, where it is mixed with the first stream, giving a mixture which flows towards the outlet 17 and the temperature of which is suicient to heat the air passing across the right-hand part of the exchanger.

At a high rate of flow, a larger proportion of the primary fluid passes through the orifices 20 by reason of the constriction 21, so that the tube 15 is heated regularly over its entire length. The constriction 21 may moreover be replaced by any other suitable ow restricting means. For example, the orifices 20 may be formed by cutting tongues in the wall of the tube 18 and turning them down towards the inside so as to reduce the cross-section of iiow of the tube 18 and to guide fluid coming from the inlet 16 towards the orifices 20.

FIGURE 4 shows a heat exchanger serving to heat a motor vehicle and comprising a tube 22 equipped with fins 23 and arranged in such manner that the Ventilating air for the vehicle interior and which is channelled between walls 24 and 25 and passes between the fins 23, is -heated by contact with such fins when hot water, entering the tube 22 at its end 22a, orws through such tube to leave at its end 22b.

In cold weather, the water circulates at a high rate of flow through the tube 22, so that the latter is heated from one end to the other. In less cold weather, the flow of hot swater delivered into the tube 22 is considerably .reduced (the rate of flow in moderate weather may be, for example, 1/10 or 1/25 of the rate of ow in cold weather) and it is advisable under these conditions to avoid the lwater cooling completely in the left-hand part of the tube 22.

To this end, there is inserted in the tube 22 of the ex changer a shorter insulating tube 26, of plastics material for example, which is provided with ribs 27 (FIGURE 5) forming spacers and keeping the tube 26 centred inside the tube 22. The tube 26 bears at its downstream end 26b on abutment means which may be a simple constriction of the tube 22, but which preferably comprises a device 28 inserted in the tube 22 and held in position by any suitable means (not shown) at the downstream end 22b of the said tube. This device 28 is constituted, for example, by a metal strip 'which is corrugated longitudinally, folded in pleated fashion, wound in a spiral or shaped in equivalent manner and may be provided as shown with perforations 28a which are preferably in staggered formation.

As will be seen in FIGURE 4, in this arrangement the upstream end 26a of the tube 26 is located at a relatively small distance from the upstream end 22a of the tube 22, and the end 26b of the tube 26 is located at a distinctly greater distance from the downstream end 2212 of the tube 22.

The hot water conveyed into the end 22a of the tube 22 is divided into a irst flow or stream 29, which iiows through the annular space 30 between the tube 22 and the tube 26 and is cooled by heating the Ventilating air, and a second dow or stream 31 which ows inside the tube 26. At the outlet of the latter tube 26, the two streams 29 and 31 are mixed and flow through the downstream portion 22c of the tube 22, passing around the strip 28 and through its perforations 28a. The strip 28 causes a turbulence, especially if the holes 28a are in staggered arrangement, and this promotes the mixing. In this way there is no risk that the water in the first stream 29, which has already been cooled in the upstream part of the tube 22, lwill ow in an annular stream against the wall of the downstream portion 22e and thus enclose the hot water in the second stream emerging from the insulating tube 26.

In moderate weather, when the -hot water is conveyed into the end 22a of the tube 22 at a rate of flow which may be very small, it is cooled a little by heating the Ventilating air between the partition 24 and the inlet 26a of the tube 26. The -first stream 29 is cooled further by heating the air over a certain distance further to the right of the said inlet 26a and arrives fully cooled opposite the downstream end 26b of the tube 26; the second stream 31 entering the insulating tube 26 is still hot, however, and remains hot on leaving the latter at 26b. The mixture of the two streams owing through the downstream portion 22a of the tube 22 is still sufficiently warm to heat the air over a certain distance to the right of the outlet 26b ofthe tube 26.

In cold weather, the hot water circulates at a high rate of flow and heats the air evenly from one end of the tube 22 to the other, the hot water of the second stream, which leaves the tube 26 at 26b, mixing with the less hot water of the tirst stream in the downstream portion 22e. The presence of the tube 26 obviously results in a pressure loss of the exchanger, but the elements can be dimensioned so that this loss of pressure does not exceed 4 to 5%.

With the last described embodiment, satisfactory results have been obtained, in all weathers, by employing a tube 26 of extruded plastics material having the profile shown in FIGURE 5, which is drawn to accurate proportions, the tube 22 having an internal diameter of 19.3 mm. and the tube 26 an internal diameter of 10.5 mm. In this embodiment, L being the useful length of the exchanger (between the partitions 24 and 25), the length of the tube 26 is equal to L/ 2, its Iupstream end 26a is spaced from the partition 24 by a length equal to L/ 8 and its downstream end is spaced from the partition 25 by a length equal to 3L/8.

FIGURE 6 shows an exchanger comprising, like that of FIGURE 1, a nest of tubes 32 having tins 33- and opening into two side pieces 34, 35, the side piece 34 for-ming the inlet header 36 and the outlet header 37 and the side piece 35 forming the intermediate header.

The tubes 32, for example, have a circular cross-section and comprise the tubes 32a, which open into the inlet header 36, and the tubes 32b, which open into the outlet header 37. Inside each of the tubes 32a there is inserted a tube 38 of insulating plastics material which is similar to the tube 26 of FIGURES 4 and 5 and provided externally with centering ribs similar to the ribs 27 of FIGURE 5. The tubes 32a are provided in their terminal portion, adjacent the side piece 35, fwith abutment means (not shown) which are formed, for example, by constrictions of the tubes 32a and against which bear the tubes 38.

The hot water, arriving under pressure through the inlet 39, which opens into the inlet header 36, is divided into a tirst stream y40, which Hows towards the intermediate header 35 through the annular spaces 41 between the insulating tubes 38 and the tubes 32a, and a second stream 42, which ows towards the said intermediate header 35 by passing through the insulating tubes 38. The second stream reaches the intermediate header 35 in a hot state and is there mixed Iwith the rst stream, which has been cooled by heating the air sweeping over the tins 33 and the walls of the tubes 32a. The mixture is at a temperature sut`n`cient to heat the air sweeping over the tubes 32b as such mixture llows from the intermediate header 35 into the said tubes 32b and towards the outlet header 37 and the outlet y43, even when the hot Water enters through the inlet 39 at a low rate 0f flow and, in consequence, the rst stream 40` reaches the header 35 completely cooled.

What is claimed is:

1. A heat exchanger comprising a heat exchange tube extending from a rst side face to a second side face and having an inlet end adjacent the yfirst side face, adapted to be fed with hot liquid at a variable ow rate, and an outlet end adjacent the second side face, for heating a stream of air flowing transversely to the tube between the side faces; a heat insulating tube slidably engaged within the heat exchange tube beyond the said side face and rib means provided externally to the heat insulating tube for centering the same lwithin the heat exchange tube, to dene a passage for the liquid between the said tubes and a by-pass for the liquid within the heat insulating tube; and an abutting member in the heat exchange tube for abutting the downstream end of the heat insulating tube at a point spaced upstream of the second side face, the abutting member comprising a sheet portion having a surface having means adapted to produce a turbulence in the liquid flowing in the exchange tube downstream of said by-pass and passage.

2. The heat exchanger of claim 1 wherein said 'first face and said second face have headers.

3. The heat exchanger of claim 2 including by-pass means between said inlet and outlet.

References Cited UNITED STATES PATENTS 773,388 10/1904 Gerken 165-97 2,942,858 6/ 1960 Stone Gurner 16S-32 2,134,665 10/1938 Karmazin 165-174 X 2,215,173 9/1940 Clarke 165-181 X 2,606,006 8/1952 Karlsson et al. 165-161 X 2,717,049 9/ 1955 Langford 165-109 X 3,270,807 9/ 1966 Steadman 165-174 2,098,830 11/1937 McElgin 165-151 2,649,698 t8/ 1953 Goldmann 165-97 X 3,030,782 4/ 1962 Karmazin 165-150 X 3,034,770 5/1962 Hiersch 165-35 ROBERT A. OLEARY, Primary Examiner.

THEOPHIL W. STREULE, Assistant Examiner.

U.S. Cl. XJR. 

